Archive for June, 2010

Retrieve the Dell PowerEdge Service Tag remotely from Windows or Linux

Saturday, June 19th, 2010

Have you ever wanted to get the Dell Service Tag from a PowerEdge machine that you don’t have physical access to? Well it’s actually quite easy as Dell make this available through the standardised Desktop Management Interface (otherwise known as DMI) framework, so you don’t even have to install any of Dell’s OpenManage tools to view it!

On a Linux system, you just need to run the following as root:

/usr/sbin/dmidecode -s system-serial-number

On a Windows box, you can accomplish the same thing from the command prompt with:

wmic bios get serialnumber

Both of these tools should be installed by default on the respective operating system. If you have some kind of super stripped down installation, then they are available from the vendor’s original media.

Intel VT Virtualisation Technology on Dell PowerEdge servers

Saturday, June 19th, 2010

Somewhat annoyingly, Dell seem to like to disable Intel’s VT (Virtualisation Technology, sometimes called VMX) in the BIOS on their Dell PowerEdge servers, which means that you can’t use the Xen hypervisor to virtualise Microsoft Windows Server without changing this setting, which requires a reboot of the server to take effect.
You can use omreport from the Dell OpenManage Server Administrator software to check whether or not you have Intel Virtualisation Technology enabled.
If you haven’t got OpenManaged Server Administrator installed, then you can enable the Dell yum repository for CentOS/Red Hat systems and install it with:

wget -q -O – http://linux.dell.com/repo/hardware/latest/bootstrap.cgi | bash
yum -y install srvadmin-base
/opt/dell/srvadmin/sbin/srvadmin-services.sh start

Once you’ve got the Dell OpenManage Server Administrator services running, you can take a look at what processor is installed in your system and what the current BIOS settings are with:

omreport chassis processors
omreport chassis biossetup

The two attributes that you’re looking for are Processor Virtualization Technology (which needs to be enabled) and Demand-Based Power Management (which needs to be disabled).

If you need to change them, then you can do this with:

omconfig chassis biossetup attribute=cpuvt setting=enabled
omconfig chassis biossetup attribute=dbs setting=disabled
omreport chassis biossetup again and then once you’ve rebooted the server you can start taking advantage of the hardware virtualisation provided by Intel’s Virtualisation Technology.

Parallels Plesk 9.5.1/9.5.2 and Greylisting

Friday, June 11th, 2010

In April’s Plesk 9.5.1 update (following on from 9.3.x – apparently Parallels can’t count so just skipped 9.4.x and 9.5.0 entirely…) they managed to seriously break one of the great Plesk 9 features for Postfix users… greylisting!

One of the big improvements when Plesk 9 was released (apart from ditching QMail!) was that it no longer relied upon unsupported third party software such as QGrey to add greylisting features. The big benefit of this was that the greylisting was tied in the with authentication of mail users, so users who authenticated to your SMTP server in order to use it as a relay automatically bypassed the greylisting filters.

The use of third party greylisting in Plesk 8.x was the source of much frustration from users who were trying to send e-mails and were getting unhelpful error messages from their e-mail clients. This puts server administrators in a difficult position; deal with the user complaints, or disable greylisting and put up with a massive increase in spam e-mail.

In Plesk 9.5.1 this feature mysteriously stopped working. At first Parallels claimed that greylisting was working as designed, but then admitted that it was a bug and they would fix it. The Plesk 9.5.2 release came and went with no fix and no word from Parallels. In the end, it was well over a month from Pleks 9.5.1 being released and the bug first being reported to a patch being available.

The fix that they have released isn’t released as a hotfix and so doesn’t show up in the normal Plesk update process either from the command line auto-installer or the Plesk web GUI’s udpate manager, nor is it applied as part of a fresh install. It’s not even on the Parallels Knowledge Base, you have to go on their forums and find it in a thread by a Parallels member of staff known as “IGorG” called “Workarounds” in the “Parallels Plesk Panel 9.5 for Linux/UNIX Suggestions and Feedback” forum.

Even once you have located the ZIP file containing the patched code and got your forum login to work long enough for you to download it without getting a “Can’t create new user ” error, Parallels have only release the fix for certain platforms (in particular, CentOS 4.x and 5.x both 32-bit and 64-bit as well as Debian 5 64-bit only) and they don’t seem to have any intention of releasing the patch for the other Linux/UNIX platforms supported by Plesk 9.x (SuSE, openSuSE, FreeBSD, Fedora, Debian 3.x & 4.x, Debian 5.x 32-bit, Ubuntu or CloudLinux).

If you are lucky enough to be on one of the supported platforms for which they have released a patch then you can download the ZIP file with the new postfix-queue files from the “official” post on the Parallels forum at http://forum.parallels.com/showpost.php?p=413387&postcount=62

Once you have copied it onto your server and extracted the contents, you should find several folders which correspond to the patched platforms (Cos4x32, Cos4x64, Cos5x32, Cos5x64 and Deb5x64), each of which has a fixed copy of the “postfix-queue” binary inside.

Back up your current postfix-queue from “/usr/lib/plesk-9.0/postfix-queue” (32-bit copies of Plesk) or “/usr/lib64/plesk-9.0/postfix-queue” (64-bit copies of Plesk) to somewhere safe and then copy the postfix-queue file from the appropriate directory over the /usr/lib/plesk-9.0/postfix-queue or /usr/lib64/plesk-9.0/postfix-queue file and restart the Postfix service.

Your authenticated users should now be able to send e-mail again without having to wait for the greylisting timers.

iOS 4 GM and Worms

Tuesday, June 8th, 2010

iOS 4 (previously iPhone OS 4.0) Gold Master has been released to developers and I am happy to report that the brilliant Worms game finally works with it on the 3GS, unlike in all of the iPhone OS 4.0 beta releases where it would launch but return you to the springboard straight away then just sit in the list of open apps in the multitasking taskbar…

Netcat saves the day!

Wednesday, June 2nd, 2010

During a botched upgrade taking an old CentOS box form 5.2 to 5.5, I ended up with a system in such a state that /lib/libselinux.so.1 and /lib64/libselinux.so.1 no longer existed. This is a major problem as it basically stops pretty much every program from working, you can’t even use cp or ls any more!

With yum and RPM unusable, SFTP/SCP/SSH clients and servers out of action and unable to use FTP or wget I thought this box was toast and was going to need a reboot and a live CD to bring it back to life.

After nosying around the system for a while to see what programs I could still run, I discovered that I could still run rsync, but this turned out to be little use as I couldn’t get RSH, SSH or RSYNC network connections in or out of the server.

The last thing I could think of was good old netcat, so I fired it up on another server with a known good copy of libselinux.so.1 and piped /lib64/libselinux.so.1 into it, then with everything crossed I piped it back out on the dying server, and lo and behold it worked and I was able to use ls again!

On the server (source) machine:

cat /lib64/libselinux.so.1 | nc -l 3333

On the client (destination) machine:

nc x.x.x.x 3333 > /lib64/libselinux.so.1

Where x.x.x.x is the IP address of the server.